The transformation of electrical power from AC to DC, and/or from one voltage to another is critical in the use of all electronic devices. Transformer and inductor circuits are used in the transmission of electrical power from the generating site to distribution points and from there to consumers. Most electrical devices require magnetic components to modify the electrical voltages especially those devices containing integrated circuits and logic elements.
As the sizes of devices continue to shrink, to improve speed, reduce weight and product size, the power transformer has become a limitation to this continual reduction. The largest single component in products such as computers has become the transformer. The most commonly used transformer consists of copper wires hand wound around a magnetic material such as iron or ferrite core. Due to the limitations of today's manufacturing methods, heat dissipation requirements and electrical efficiency, the size of magnetic components cannot be significantly further reduced.
A number of alternative magnetic structures have been developed over the last few years, with a number of deficiencies, most notably the prospect of the further reduction in size and improved efficiency. Examples of these include U.S. Pat. Nos. 4,543,553, 4,689,594, 5,126,714 and 5,279,988.
U.S. Pat. No. 4,543,553 describes a magnetic inductor structure. The coil is achieved by passing current through a series of successive magnetic layers, using one conductor per via to create the coil.
U.S. Pat. No. 4,689,594 defines a structure which operates as an inductor, the simplest type of magnetic device. In this structure, magnetic material is utilized with through holes. It is important to note that once again, only one conductive element is utilized per through hole.
Another magnetic structure is described in U.S. Pat. No. 5,126,714 in which the transformer is formed from two layers of magnetic material with magnetic posts connecting the two layers. The coil is formed on a planar sheet using printed circuit technology. Once assembled, the posts extend through the structure, making the magnetic elements. The through vias used are for electrical connection to the external contacts and are single conductor elements. U.S. Pat. No. 5,279,988 also utilizes single conductor vias for interconnection through the multilayer magnetic structure.
U.S. Pat. No. 5,300,911, "Monolithic Magnetic Device with Printed Circuit Interconnections" describes a magnetic device in which a slab of magnetic material which contains an array of through holes that permit the connection of electrical circuits on each side, forming a "coil". These through connections are formed by using electroplating technology to metallize the through hole to form two concentric, electrically isolated, conductive elements which forms the connection to each of two separate wiring structures on each side of the magnetic element thus forming a secondary and primary winding layer. The difficulties with this approach are the limitation in the wiring density and the performance due to the technologies required to make two concentric electrically conductive elements which are electrically isolated by electroplating techniques.